OP ARTS AND SCIENCES. 21 



Fig. 7. Head of same species, a couple of days after hatching, before any 

 movement of translation or of rotation of either eye has com- 

 menced. The two eyes symmetrically placed at the extremities of 

 a transverse axis at right angles to the longitudinal axis of the 

 Flounder. 



„ 8. Shows the position of the eyes of the young Flounder from the left 

 side, where the right eye projects beyond the ridge of the frontal 

 bone. 



„ 9. Shows the position of the right eye, seen from the right side, at about 

 the time the lower edge of the orbit has reached the summit of the 

 edge of the frontal bone. 



„ 10-13. Show in regular succession the gradual passage of the eye from 

 the stage of fig. 9 until it has reached, in fig. 13, the position it re- 

 tains on the adult entirely on the left side of the body ; the space 

 between the eyes separated by tlie frontal ridge becoming less in 

 each specimen with advancing age. 



PLATE VI. 



PSEUDORHOMBUS MELANOGASTER StEIN. MaSS. FiSH ReP. 1872, p. 47. 



Platessa oblonga Storer PL XXXI. fig. 2. 



Fig. 1. Young specimen, just hatched from the egg. The yolk mass project- 

 ing below the outline of the lower surface ; the dorsal embryonic 

 fold much wider than the anal embryonic fin ; the pigment spots 

 are confined to the dorsal edge of the brain, and to the muscular 

 band above the notochord. 



„ 2. Embryo two days old. The yolk mass projects but little beyond the 

 line of the lower surface. Large prominent pigment spots extend 

 over the whole body, with the exception of a small portion of the 

 tail, which is left bare from the earliest stages (fig. 1), and remains 

 bare for some time yet, thus giving an excellent specific distinction 

 for readily distinguishing the young of this species from other 

 species of embryos about in the same stages. The snout has become 

 more pointed than in the preceding stage, the dorsal embryonic 

 fold has lost much of its width, and in consequence the young fish 

 resembles a tadpole much less than in the preceding stage. 



„ 3. Represents the same embryo on the fifth day after hatching. The prin- 

 cipal changes consist in the form of the head, the prolongation 

 of the lower jaw well in advance of the upper one, the presence 

 of large pectorals, the increase of the stomach, and a very slight 

 tendency to heterocercality in the tail. 



„ 4. Somewhat older embryo. The stomach and alimentary canal have 

 greatly increased in size, the air-bladder has become prominent, 

 the body has greatly increased in width, the tail is decidedly more 

 heterocercal.than in the previous stage figured, and the right eye 

 shows a slight tendency to move upward and forward towards the 

 anterior edge of the snout. 



